In general, transesterification between a cyclic carbonate and ethanol is widely known as a method for producing diethyl carbonate (see, for example, Patent Literature 1 and Patent Literature 2).
For example, Patent Literature 1 describes a method in which, using propylene carbonate as a cyclic carbonate, a mixture of propylene glycol as a reaction by-product with dimethyl carbonate as the objective substance is obtained, and then the obtained mixture is separated by further distillation to obtain dimethyl carbonate. Patent Literature 2 describes a method in which, using ethylene carbonate as a cyclic carbonate, ethylene carbonate is transesterified with two or more types of alcohols in the same reactor to produce a symmetrical dialkyl carbonate and an asymmetrical dialkyl carbonate. Patent Literature 2 describes a method in which, after the reaction, a low-boiling fraction containing, as main components, a symmetrical dialkyl carbonate and an asymmetrical dialkyl carbonate as objective substances, and alcohol as a raw material for production is separated from a high-boiling fraction containing, as main components, an alkylene carbonate as a raw material for production and an alkylene glycol as a reaction by-product by distillation. This literature describes that purification additionally includes a means for extraction separation, since various alkyl glycol ethers, such as ethyl glycol ether to be by-produced during the reaction, are mixed in the low-boiling component, in addition to the objective symmetrical dialkyl carbonate and asymmetrical dialkyl carbonate, and also these alkyl glycol ethers cannot easily separated by distillation because of having an azeotropic relationship with the objective alkyl carbonate.
Several methods for industrially producing diethyl carbonate by transesterification using dimethyl carbonate (DMC) as a raw material for production have been reported (see, for example, Non Patent Literature 1).
For example, Non Patent Literature 1 describes using, as a transesterification catalyst, Lewis acid compounds, such as yttrium triflate and samarium triflate, dimethyl carbonate is reacted with ethanol to synthesize diethyl carbonate.
Most methods for producing diethyl carbonate using a cyclic carbonate or dimethyl carbonate (DMC) as raw materials for production comprise transesterification utilizing chemical equilibrium reaction. In order to allow this reaction to proceed efficiently, a method for distilling an alkylene glycol and methanol as reaction by-products is carried out. However, for example, since DMC forms an azeotropic mixture having the general composition of 70% methanol and 30% DMC with methanol under atmospheric pressure, and complete reaction of DMC is substantially impossible when this type of transesterification is carried out, DMC is distilled out of the reaction system together with methanol in an actual reaction, resulting in insufficient DMC conversion rate or low industrial reproducibility. Therefore, a further need for a method for separating and removing methanol from an azeotropic mixture of DMC with methanol is described (see, for example, Patent Literature 3).